1. Field of the Invention
The present invention relates to an improved socket assembly for use with an integrated circuit device or package (IC), which assembly comprises a socket body, a plurality of contact elements, a top plate and a cam member for opening the contact elements upon movement of the top plate toward the body, and in one aspect to an improved cam design.
2. Description of the Prior Art
Top loading sockets for integrated circuit devices or packages (IC's) are known and are used to connect IC's to printed circuit boards for test or burn-in by automated operations, or for the functional application affording the replacement of the IC without subjecting other components on a printed circuit board or the like to heat, to afford the removal or replacement of the IC. To this end there have been sockets designed to afford the top-loading of the IC, whether the IC is leaded or leadless.
Examples of the sockets or carriers of the prior art using a cam member to move the contact members to an open position include applicant's own U.S. Pat. No. 4,993,955 disclosing a carrier for an IC device which has leads and which has a cam member inserted on the socket body to withdraw the contacts, against their inherent biasing force, from a contacting position to a retracted position upon the movement of the top plate toward the socket body. There are other patents which show a top load socket having similar top load characteristics but these sockets have the cover engaging each of the plurality of contacts directly to retract the same.
Another known application disclosing cam members for opening the contact elements of a top load socket is Japanese Laid-Open application No. 4-154065 having a Laid-Open date of May 27, 1992. The structure of FIGS. 8(A) and 8(B) are the only views showing a cam design wherein the cam is positioned above the contact elements and serves to move them from an operating position to an open position. In this example, however, the cam is secured to the contact element and is fulcrumed about a member disposed above the center of the spring portion of the contact elements and lifts the contacting portion from the IC lead. The cam is apparently operated by the outer edge of a top plate in a manner corresponding to that shown in FIGS. 4(A), (B) and (C) and similar to the top plate described in U.S. Pat. No. 4,846,703.
A difficulty with the prior art socket assemblies using the cam design is the fact that they are difficult to manufacture. This difficulty arises due to the fact the contacts have to be inserted into the anchoring recesses in the socket body and then the contact elements have to be moved to a retracted position to permit assembly of the cam member into the cradle. This is the case with the assembly described in U.S. Pat. No. 4,993,955. Thereafter, the cover plate and the cam member serve to open the contacts with ease to afford the insertion and/or removal of the IC device. Additionally, the cam designs have used the cam followers located at the opposite ends of the cam member and there was the possibility of a torsional loading being applied to the cam member if the opening forces were not evenly applied to the top plate to retract the contact elements to the open position.
The socket assembly of the present invention affords a structure which is easily assembled without danger of overstressing or bending the contact elements in assembling the cam member.
The socket assembly of the present invention affords positive movement of the contacting portion of the contact.
The socket assembly of the present invention affords a cam member design which evenly distributes the actuating force along the length of the cam member. The new design restricts torsional distribution of the loading force on the cam member.
The contacts have a profile which affords a substantial reduction in the cantilevered portions which have to carry the load for retracting the contact elements.
The socket assembly is of a design which reduces the number of dimensionally critical features on each part.